The long-term goal of our research is to provide guidance to clinicians as they choose among alternative ART regimens in patients who have HIV and comorbid conditions. We aim to study the comparative effectiveness and cost effectiveness of ART regimens in two populations of high importance in the VA: patients who have HIV and chronic kidney disease (CKD), and patients with HIV and hepatitis C virus (HCV) co-infection. These comorbidities are of special concern of their high prevalence and substantial morbidity and mortality. We also propose to use the VA HIV clinical case registry (CCR) to evaluate utilization, practice patterns and cost-effectiveness of three new classes of HIV antiretroviral agents that have been introduced recently. These agents are highly effective, but expensive, and our work to date indicates that whether they are cost effective depends on how they are used with other antiretroviral agents. Our study has three specific aims: 1. To evaluate the comparative effectiveness and cost effectiveness of treatment for HIV- positive individuals with risk factors chronic kidney disease o established chronic kidney disease. a. We will use the VA HIV Clinical Case Registry (CCR) of more than 55,000 HIV patients to assess whether exposure to specific antiretroviral drugs or regimens is associated with poorer outcomes in patients with risk for kidney disease or established kidney disease. b. We will develop a cost-effectiveness model to evaluate how alternative antiretroviral regimens influence long-term outcomes, including all-cause mortality, HIV-specific morbidity and mortality, morbidity and mortality from CKD with 2. To evaluate health outcomes, costs and comparative effectiveness and cost effectiveness of HIV antiretroviral regimens in HIV-infected individuals co-infected with HCV. As new antiviral agents become available for treatment of HCV, we will also evaluate their cost effectiveness. 3. To evaluate the practice patterns, utilization and cost effectiveness of the use of new antiretroviral - including but not limited to second generation protease inhibitors, integrase inhibitors, and entry inhibitors - in veterans with HIV.